Starship For Gameboy

This is a Gameboy game I have been working on recently. I would love to hear some feedback on it as I would like ideas for improving the game.

Web browser key binds:

Up - Up Arrow

Down - Down Arrow

Left - Left Arrow

Right - Right Arrow

A - Z Key

B - X Key

Select - Right Shift

Start - Enter

Game Info:

• There are two modes, arcade and free play. In arcade, you play timed levels and progress through an increasingly difficult gauntlet of 30 levels.  In free play, you play an infinitely long level on the difficulty of your choosing. Pretty much all of the same rules of the main game apply here.

• There are two types of enemies, static enemies and follower enemies. The static enemy stays in one place and shoots at you. The follower enemy does just as the name implies, it follows your location based on the axis it is placed on. 

• To progress, you must survive the specified amount of time from the beginning of the level.

• Avoid the lasers being shot at you
  

• Do not touch the dark green walls, they will kill you

• You have 3 lives per level

• There are 30 levels, with difficulty increasing every 10 levels

• You gain a checkpoint at every 10th level

• If you game over you will go back to your most recent checkpoint